Patients with borderline personality disorder and rejection-sensitive dysphoria participated in a program of clinical and biological evaluation and psychopharmacologic treatment. In addition to having labile moods and behavioral dyscontrol, these individuals were found to have a high incidence of psychosensory symptoms similar to those seen in complex partial seizures. There was a high incidence of non-specific electroencephalographic (EEG) abnormalities. One-quarter of our patients had gross structural abnormalities on computerized axial tomography (CT) scans. Procaine infusions frequently produced dysphorias similar to those occurring naturally, and activated a high frequency band of EEG activity over the temporal lobes. Group therapy employing small, diagnostically homogenous groups may have significant value in the treatment of borderline personality disorder. A year-long, double-blind, placebo-controlled cross-over study of the effects of medication on mood and dyscontrol behavior suggested that alprazolam (a triazolo-benzodiazepine) may disinhibit these individuals, resulting in serious behavioral dyscontrol; that low-dose trifluoperazine (an antipsychotic), is not consistently different from placebo; that carbamazepine (an anticonvulsant) significantly decreases dyscontrol and produces improvement in physician (but not patient) ratings; and that tranylcypromine (a monoamine oxidase inhibitor with antidepressant actions) produced significant global improvement in mood and had variable effects on behavioral dyscontrol.